A low-pressure area spinning up over west-central Bay of Bengal and neighbourhood on Monday persisted around the same region towards the evening, according to an update from India Meteorological Department (IMD).

According to a senior official of the National Centre for Medium Range Weather Forecasting, the system was located on or just off the Andhra Pradesh coast and was expected to move very slowly to the west.

COULD INTENSIFY

While doing so, it is expected to intensify at least one round into a well-marked 'low', he said; there is even an outside chance it could ramp up to a depression, given the slow grind.

The European Centre for Medium-Range Weather Forecasts (ECMWF) and a host of other international weather models project the system as meandering across the peninsula to emerge into the Arabian Sea around October 3.

The Bay 'low' set up the western-most front of a massive trough of low pressure spanning the Bay of Bengal and extending into the adjoining Indo-China, the South China Sea and the west Pacific.

Apart from the 'low' in the Bay, the trough is hosting at least three distinct areas of turbulence - raging Typhoon Ketsana in the South China Sea and Tropical Depressions No 18 and 19 in the west Pacific, east of the Philippines.

Ketsana is expected to make landfall over Vietnam in the next 24 hours, according to the London-based Tropical Storm Risk Group. It may go on to 'lit up' the Bay for one more time, says the ECMWF.

The fresh 'low' may form off the Andhra Pradesh coast by October 1 and travel in a west-northwest direction to emerge into the Arabian Sea by October 5.

This could trigger another round of widespread to fairly widespread showers all over the peninsula, according to forecasts available on Monday.

NOT UNUSUAL

The late-September activity in the Bay of Bengal is not exactly unusual but does not jell with a situation where an ongoing El Nino in the equatorial central and east Pacific has already spoilt the just-concluding monsoon.

The Climate Prediction Centre (CPS) of the US National Weather Services attributed this to tropical sub-seasonal variability (climate variations that recur in cycles) that cannot be predicted accurately.

Meanwhile, the IMD has forecast isolated heavy to very heavy rainfall over Andaman and Nicobar Islands, coastal Orissa, West Bengal and coastal Andhra Pradesh during the next two days.

Isolated rain or thundershowers are likely over Konkan, Goa and Madhya Maharashtra during the next two daysand increase thereafter. Mainly dry weather will prevail over central India during this phase but isolated rain or thundershowers are likely thereafter.

Satellite pictures on Monday showed convective clouds over many parts of Bay of Bengal, Andaman Sea, Orissa and West Bengal. The three days ending October 3 areforecast to witness scattered to fairly widespread rain fall activity with isolated heavy falls over the west coast and peninsular India.

Towards the north, the monsoon has withdrawn from the entire Jammu and Kashmir, Himachal Pradesh, Punjab, Haryana, many parts of Rajasthan and some parts of Uttarakhand, west Uttar Pradesh and north Gujarat.

WITHDRAWAL LINE

On Monday, the withdrawal line passed through Uttarkashi, Aligarh, Sawai Madhopur, Udaipur and Naliya, the IMD said.

The Chennai Met Centre said in an update that the monsoon has been active over Kerala and north interior Karnataka during the 24 hours ending on Monday morning.

Rainfall occurred at most places over north interior Karnataka; at many places over Kerala and coastal Karnataka; and at a few places over Telangana, Rayalaseema and south interior Karnataka. Isolated rainfall was reported from Tamil Nadu and coastal Andhra Pradesh.

Forecast for the next two days said that rain or thundershowers are likely at many places over Kerala, coastal Andhra Pradesh, Telangana and coastal Karnataka.

Thundershowers are likely at a few places over Tamil Nadu, Puducherry, interior Karnataka and Rayalaseema while they will be isolated over Lakshadweep.

A warning valid for the next two days said that isolated heavy rain is likely to occur over Kerala and north coastal Andhra Pradesh.